1. Field of the Invention
This invention relates to selected acid generating agents useful in radiation-sensitive patterning compositions. The invention relates to such radiation-sensitive patterning compositions as well as methods of imaging radiation-sensitive elements containing such radiation-sensitive patterning compositions.
2. Brief Description of Art
Thermally sensitive, negative working printing plates are generally made with radiation-sensitive patterning compositions that are imaged on a substrate. These patterning compositions commonly contain radiation-sensitive material that is a mixture of an acid generator, a cross-linking resin or compound, a binder resin and an infrared (IR) absorber. Many of the acid generators previously employed in these patterning compositions either contain ozone depletion elements such as fluorine or contain heavy metal such as antimony (Sb) or arsenic (As), which may cause serious environmental contamination problems. Also, some of these previously used acid generators produce volatile acids (e.g., HF, HCl, HBr, HI) that can be easily volatized and lost under conditions of thermal imaging and subsequent optional baking, thereby reducing the cure rate. Such volatile acid loss decreases the efficiency of the printing plates.
Examples of these prior art acid generators are reported in the following:
U.S. Pat. No. 4,708,925 (Newman) describes a photosolubilizable composition comprising an alkali-soluble phenolic resin and an onium salt. The onium salt imparts a solvent resistance to the phenolic resin that is removed upon exposure to radiation thereby providing a solubility differential between exposed and unexposed areas of the composition. Suitable iodonium salts include iodonium, sulphonium, bromonium, chloronium, oxysulphonium, sulphoxonium, selenium, telluronium, phosphonium and arsenium salts. Preferably the acid from which the anion is derived has a pKa<5. Suitable inorganic anions include halide anions, bisulfate, tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate and hexafluoroantimonate. Suitable organic anions include those of the formulae: R1COO− and R1SO3−, in which R1 is an alkyl or aryl. Again, this reference does not teach or suggest the particular acid generators of the present invention.
U.S. Pat. No. 5,372,907 (Haley et al.) describes a radiation-sensitive patterning composition comprising a mixture of (1) a resole, (2) a novolak resin, (3) a latent Bronsted acid (i.e., acid generating agent) and (4) an infrared absorber. In the specification, the latent Bronsted acids in the invention include onium salts, in particular iodonium, sulfonium, phosphonium, selenium, diazonium and arsenium, with anions such as hexafluorophosphate, hexafluoroantimonate and trifluoromethane sulfonate. However, this reference does not disclose or suggest any latent Bronsted acids of the present invention.
U.S. Pat. No. 5,919,601 (Nguyen et al.) describes a printing plate composition comprising a thermal-activated acid generator; a cross-linking resin; a binder resin comprising a polymer containing reactive pendant groups selected from hydroxyl, carboxylic acid, sulfonamide, and alkoxymethylamide; and an infrared absorber. The composition claims that acid generator is selected from halo alkyl substituted S-triazines and salts containing an onium cation and non-nucleophilic anion, wherein the onium cation is selected from iodonium, sulphonium, phosphonium, oxysulphoxonium, oxysulphonium, sulphoxonium, ammonium and diazonium; the non-nucleophilic anion is selected from tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, hexafluoroarsenate, triflate, tetrakis(penta-flurophenyl)borate, pentafluoroethyl sulfonate, p-methylbenzenesulfonate, ethyl sulfonate, trifluro-methylacetate and pentafluoroethyl acetate. This reference does not disclose or suggest the acid generators of the present invention.
U.S. Pat. No. 5,945,250 (Aoai et al.) teaches a positive-type photosensitive composition that contains a polymeric sulfonate resin of an iodonium or sulfonium salt and which generates a sulfonic acid upon receiving light. This light-exposed resin increases in solubility in an alkali developer to provide a positive resist pattern.
U.S. Pat. No. 5,965,319 (Kobayashi) describes certain onium salt compounds having sulfonic acid as the counter ion to generate sulfonic acid decomposed by light or heat. These onium salts include diazonium sulfonates represented by the following structural formula:Ar1—N2+R1—SO3−wherein R1 represents a hydrocarbon group having 20 or fewer carbon atoms which may be substituted; and Ar1 represents an aryl group having 20 or fewer carbon atoms which may be substituted. This reference does not teach or suggest any of the acid generators of the present invention.
U.S. Pat. No. 6,042,987 (Kobayashi) describes a photosensitive negative image recording material for printing plate having a image recording layer containing a compound which is degraded by the action of light or heat to generate an acid, including an onium salt having a halide, ClO4−, PF6−, BF4− or sulfonate as a counter ion. There is no knowledge of using the compounds with formulae (I)-(III) in the invention.
WO 00/17711 (IBF Industria Brasileira De Filmes S/A) describes a composition comprising a dual polymer system, an infrared absorbing material, an acid generating compound, and an acid stabilizing compound. The acid generating compounds named therein include, as anions, chloride, bisulfate, hexafluoroantimonate, hexafluorophosphate, tetrafluoroborate, methane sulfonate and mesitylene sulfonate. However, this reference does not teach or suggest acid generating compounds in the present invention.
Accordingly, there is a need for better acid generators that can be used in radiation-sensitive patterning compositions that do not contain environmental questionable elements or produce undesirable volatile acids, yet have a high photolysis efficiency and good photo sensitivity. The present invention provides a solution to that need. In particular, the present invention provides an improved cure rate, processing latitude, processing robustness and long shelf life while maintaining moderate energy requirements of the acid generation step.